Rotary retort furnace

ABSTRACT

A heat treating furnace in which several cylindrical retorts are clustered in a circle and are adapted to revolve in unison about a central axis in a heating chamber. Workpieces delivered into the chamber are distributed into the retorts and are exposed to heated gas as the cluster is revolved to cause the workpieces to advance through and tumble within the retorts.

United States Patent [191 Wul Aug. 13, 1974 [5 ROTARY RETORT FURNACE 1,964,344 6/1934 Fasting 432/118 x 3,279,775 10/1966 Roubal [75] Wulf, Rockfmd 3,556,498 H1971 Sheahan 432/118 [73] Assignee: Alco Standard Corporation, Valley Forge, Pa. Primary Examiner.lohn J. Camby [22] Filed: Oct 29, 1973 ilgftrgfygg1egltfigFlrmW0lfe, Hubbard, Leydig [21] Appl. No.: 410,823

[57] ABSTRACT [52] US. Cl 432/103, 432/1 l8, 432/124 A heat treating furnace in which several cylindrical [51] Int. Cl. F27b 7/04, F27b 7/14 re orts are clustered in a circle and are adapted to re- [58] Fi ld of S arch 432/1 1, 103, 106, 108, volve in unison about a central axis in a heating cham- 432/118, 124, 154 ber. Workpieces delivered into the chamber are distributed into the retorts and are exposed to heated gas [56] R f ren Cit d as the cluster is revolved to cause the workpieces to UNITED STATES PATENTS advance through and tumble within the retorts.

1,885,845 11/1932 Lindhard 432/ 106 14 Claims, 5 Drawing Figures /0 f I! a 2/ I! I? I y v/fl g j l I, 4

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sum 30F a BACKGROUND OF THE INVENTION This invention relates generally to apparatus for heat treating workpieces and, more particularly, to a rotary retort heat treating furnace. In such a furnace, loose workpieces are loaded into a drum-like retort which is mounted to rotate about a horizontal axis within a chamber adapted to be heated to high temperatures. As the retort is rotated, means such as spiraled flights within the retort advance the workpieces gradually through the retort while causing the workpieces to tumble continuously toward the bottom of the retort during their advance so as to fully expose the workpieces to heat and treating gases.

The main drawbacks of presently commercially available rotary retort furnaces are their relatively low production rates and the comparatively short service lives of their retorts. The production rate of the furnace can be increased by increasing the length of the retort but, under such circumstances, the service life of the retort is reduced still further since the longer retort tends to sag and flex more severely under the weight of the tumbling workpieces and ultimately fails as a result of fatigue. In addition, increasing the length of the retort increases the length, and thus the cost, of the overall furnace and also requires a greater amount of floor space to accommodate the furnace.

SUMMARY OF THE INVENTION The general aim of the present invention is to provide a new and improved rotary retort furnace which, when compared with prior retort furnaces of the same length, possesses a longer service life and is capable of higher production rates.

A more detailed object is to achieve the foregoing through the provision of a novel furnace having a plurality of retorts uniquely arranged in a cluster and supported to revolve around a central axis, the load capacity of the cluster being significantly greater than that of a single retort of comparable length and diameter.

An-additional object is to take advantage of the clustered arrangement of the retorts to enable the retorts to be supported in a rigid manner and along substantially their entire length so as to reduce sagging and fatigue of the retorts. By virtue of their rigid support, the retorts can be made of comparatively thin material or of material which otherwise would be incapable of withstanding the load imposed by the workpieces.

Still another object is to provide a rotary retort furnace in which more efficient heating of the workpieces is achieved, the heating being effected by convection as well as radiation so that the workpieces are continuously washed with hot gas as they are advanced through and tumbled within the retorts.

The invention also is characterized by the provision of unique means for loading workpieces into the furnace and for distributing the workpieces substantially uniformly into the clustered retorts.

These and other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross-section taken vertically through a new and improved heat treating furnace embodying the novel features of the present invention.

FIG. 2 is an end view of the furnace as seen from the left of FIG. 1.

FIG. 3 is a fragmentary cross-section taken substantially along the line 3-3 of FIG. 2.

FIGS. '4 and 5 are enlarged fragmentary crosssections taken substantially along the lines 4-4 and 5-5, respectively, of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings for purposes of illustration, the invention is embodied in a heat treating furnace 10 of the rotary retort type. Such a furnace is typically used to heat small workpieces such as steel bearing balls (not shown) to high temperatures (e.g., 2,000F.) in the presence of a non-oxidizing gas. The workpieces are loaded loose into the furnace from one end thereof and are advanced toward the other end while being continuously tumbled within the furnace so as to fully expose the surfaces of all the workpieces to the heat and gas and thereby promote uniform heat treating of the workpieces.

In the present instance, the furnace 10 includes an outer steel enclosure or jacket 11 whose lower half is rectangular in cross-section (see FIG. 2) and whose upper half is shaped as .a half cylinder, the jacket being supported on channels 13 (FIG. 1). Attached to the front end of the jacket is an upright end wall 14 to which is secured an inwardly projecting cylindrical shell 15 whose outer surface is spaced from the inner surface of the jacket to reduce the transmission of heat between the shell and the jacket. A similar shell 16 is attached to an upright end wall 17 at the rear of the furnace and, as shown, the two shells and two end walls are interiorly faced with a relatively thick lining of high temperature insulating material such as refractory brick 19. The two brickwork sections 19 are generallydish-shaped and are positionedsuc'h that a heating chamber 20 is defined within and between the two sections.

In accordance with the present invention, several rotary retorts 21 are arranged in a cluster within the chamber 20 and are supported to revolve in unison around a central axis 23 (FIG. 4). The workpiece-s are delivered into successive ones of the retorts as the latter revolve and then are advanced through the retorts while being tumbled and exposed to heated gas. By virtue of providing a plurality of retorts 21, :the load capacity of the furnace 10 is increased significantly above that of furnaces having a single retort with a length and diameter comparable to that of the cluster .and thus higher production rates can be obtained. In addition, the unique clustered arrangement of the retorts enables each retort to be supported ruggedly so :as .to reduce the tendency of the retorts to sag downwardly under the weight of the workpieces, Accordingly, the retorts are subjected to less fatigue stress and hence, even when the retorts are made of relatively low strength material, they possess a relatively long service life and require replacement less frequently than the retorts of ;pr'ior furnaces.

More specifically, eight retorts 21 herein are incorporated into the furnace and each is defined by a cylindrical tube made of stainless steel and positioned with its axis 24 (FIG. 4) extending parallel to the central axis 23. The retorts 21 are clustered in a circle around the central axis 23 and are sized and located such that adjacent sides of adjacent retorts are tangent to and in supporting contact with one another. A stainless steel cylinder 25 is telescoped into the retort cluster and is located with its outer surface tangent to the inner sides of the retorts, the cylinder having a length somewhat greater than one-half the length of the retorts and having its rear end substantially coextensive with the rear ends of the retorts. The retorts are anchored rigidly to the cylinder and thus the cylinder connects the retorts to one another as well as supporting the inner sides of the retorts along part of the length of each retort. The cylinder also serves another important function which will be explained subsequently.

As shown in FIGS. 1 and 4, the retort cluster istelescoped rigidly into an outer drum 26 which includes a ring 27 of refractory brick or other high temperature insulating material. The inner surface of the brick ring 27 is tangent to and rigidly supports the outer sides of the retorts 21 along substantially the entire length of each retort while the outer surface of the ring is encircled by a cylindrical steel shell 29 (FIG. 1) located between the end shells and 16. Several angularly spaced pins 30 are anchored to the shell 29 and extend radially through the brick ring and into the retorts in order to hold the drum and the retorts in angularly and axially fixed relation.

The drum 26 defined by the brick ring 27 and the shell 29 is adapted to be power-rotated about the central axis 23 and, when so rotated, the drum causes the retorts 21 to revolve in unison about the axis. To support the drum for rotation, four rollers 31 (FIGS. 1 to 3) are journaled on a stationary frame (not shown) located beneath the drum and mounted on the bottom wall of the outer jacket 11. The rollers are located with their axes extending parallel to the central axis 23 and are positioned such that the two front rollers engage and cradle a steel band 33 extending rigidly around the front portion of the shell 29 while the two rear rollers cradle a similar band 34 encircling the rear portion of the shell.

Power for rotating the drum 26 is derived from an electric motor 35 and reducer 36 supported on the outside of the front wall 14 and serving to drive a shaft 37 which extends through the front wall and beneath the chamber 20. The shaft 37 is coupled to a shaft 39 (FIG. 3) extending between and keyed to one of the front rollers 31 and the alined rear roller. Accordingly, those two rollers are power rotated and frictionally engage the bands 33 and 34 to cause the drum 26 and cylinder 25 to rotate about the axis 23 while simultaneously causing the retorts 21 to revolve about the same axis.

In carrying out the invention, unique means are provided for loading the workpieces into the chamber from outside of the furnace 11 and for distributing the workpieces substantially uniformly into the eight retorts 21 as the latter revolve. Herein, these means comprise an upwardly opening loading and storage hopper 40 (FIG. 1) secured to the upper portion of the outer side of the rear wall 17 and communicating at its lower end with an elongated conveyor in the form of a chute 41. The latter is inclined downwardly and forwardly from the hopper and extends into the chamber 20 through an opening 43 formed through the rear wall 17 and the adjacent brick section 19. To control the delivery of workpieces from the hopper 40 into the chute 41 and to reduce the escape of heat from the chamber 20 through the chute, a selectively operable gate 44 is supported on the outer side of the rear wall 17 and is adapted to be raised and lowered between closed and open positions by a hydraulic cylinder 45. The gate is suitably mounted and arranged to divide the chute into upper and lower sections and is formed with an opening 46 which allows the workpieces to fall from the upper section and into the lower section when the gate is in its open position. When closed, the gate forms a partition between the upper and lower chute sections and blocks off the opening 43 so as to retard the escape of heat from the chamber 20.

As shown in FIG. 1, the chute 41 extends through the rear end of the cylinder 25 and its lower discharge end is located in a central distributing area defined within the interior of the cylinder. Workpieces delivered into the forward end portion of the cylinder by the chute are advanced rearwardly within the cylinder and then are distributed into the retorts 21 adjacent the rear ends of the retorts. For this purpose, eight curved vanes 47 (FIGS. 1 and 4) are spaced angularly around and are welded to the interior of the cylinder 25 and are spiraled around and along the cylinder in such a direction as to convey the workpieces rearwardly or in the direction of the arrow 48 shown in FIG. 1 when the cylinder is rotated counterclockwise (FIG. 4).The rear end of each vane is located directly alongside a radially projecting tube 49 (FIG. 4) welded to and extending outwardly from the rear end of the cylinder 25 and defining a hole leading from the cylinder. The eight tubes are spaced angularly from one another in accordance with the spacing of the retorts 21 and are telescoped into holes 50 extending radially through the rear ends of the retorts so as to establish communication between the cylinder and the retorts while causing the cylinder to rotate when the retorts are revolved. Accordingly, the workpieces are advanced rearwardly by the vanes 47 and drop through successive tubes 49and into successive retorts 21 as the latter revolve into a position below the cylinder. In this way, the workpieces delivered by the chute 41 are distributed into the eight retorts in a substantially uniform manner.

In order to advance the workpieces through the retorts 21, an auger-like screw or flight 51 (FIGS. 1 and 4) is welded to the inside of each retort and is spiraled continuously around and along the retort from one end thereof to the other. Each time a retort makes one revolution about the central axis 23, the workpieces in the retort are advanced in a forward direction (see the arrow 53 in FIG. 1) by the spiraled flight in the same manner as would be the case if the retort were rotated through 360 about its'own axis 24. In other words, any given point on each flight turns through one revolution about the axis 24 of the associated retort 21 as the retort is revolved a full turn about the axis 23 and thus the workpieces continuously advance in a forward direction and, at the same time, continuously tumble as a result of returning to the lowermost surface of the revolving retort. By virtue of flights 51, the workpieces which drop into each retort along the lower path of its orbit are advanced forwardly of the tube 49 and the hole 50 well before the time the retort reaches the upper path of its orbit and thus the workpieces will not fall back downwardly into the distributing cylinder 25.

As the workpieces complete their advance, they are discharged out of the forward ends of the retorts 21 and fall into an upright chute 54 (FIG. 1) located in the bottom portion of the furnace l and leading to a quench tank (not shown). In order to insure that the workpieces will drop out of each retort only when the latter is adjacent the chute 54, the forward end of each retort is partially closed by a ring 55 (FIG. formed with a radially extending cut out 56 which opens downwardly toward the chute when the retort moves along the lowermost portion of its orbit. Thus, the ring captivates the workpieces in the retort until the retort revolves downwardly to a position adjacent the chute.

Further to the invention, the workpieces are heated efficiently by convection and are thoroughly washed by hot gas as they tumble through the retorts 21. To heat the workpieces, groups of electric resistance heating elements 57 (FIGS. 1 and 2) are located in the chamber 20 at each end of the drum 26. The heating elements herein are generally ring-shaped and are sufficiently large in diameter as to be in substantial alinement with the retorts when the heating elements are arranged as shown in FIG. 1. Gas for forming the atmosphere of the furnace is admitted into the chamber 20 through a pipe 59 (FIG. 1) at the rear end of the furnace and is circulated past the heating elements and through the retorts 21 and the cylinder 25 to heat the workpieces therein. As shown in FIG. 1, a motor-driven fan 60 is located at the forward end of the chamber 20 and is alined with a frusto-conical sleeve 61 on the forward end of the cylinder 25. When the fan is rotated, the gas is drawn forwardly through the cylinder and is circulated past the front heating elements 57. The gas then flows reversely through the hollow retorts and past the rear heating elements before re-entering the rear end of the cylinder. Accordingly, the workpieces are intimately exposed to the heated gas not only during their advance through the retorts 21 but also during the time they are in the distributing cylinder 25. Thus, the latter serves as an additional retort within the furnace 10.

From the foregoing, it will be apparent that the present invention brings to the art a new and improved furnace in which several retorts 21 are arranged in a circular cluster and are supported to revolve about a common axis 23. With eight retorts arranged in the cluster, the production capacity of the furnace is approximately four times as great as that of a furnace of comparable size but having only a single retort which rotates about its own axis. The retorts are backed on their inner sides by the distributing cylinder 25, are disposed in side-by-side contact so as to support one another, and are supported rigidly on their outer sides and over their full lengths by the outer drum 26. Thus, the retorts are supported in such a stiff manner that they can be made of relatively thin metal or even ceramic material and still will experience a comparatively long service life.

1 claim as my invention:

1. Heat treating apparatus comprising a walled enclosure defining a chamber, a drum supported within said chamber to rotate about a substantially horizontal axis, a cluster of generally cylindrical retorts telescoped rigidly into and spaced angularly around said drum and located with their axes extending substantially parallel to the axis of the drum, said retorts being spaced radially from the axis of said drum thereby to leave a central distributing area between the retorts, mechanism for rotating said drum thereby to cause said retorts to revolve around the axis of the drum, means operable during rotation of said drum to deliver workpieces into said distributing area from outside of said chamber and to distribute said workpieces into said retorts, means within said retorts for advancing said workpieces through the retorts as the latter revolve about the axis of said drum, and means within said chamber for heating said workpieces as the workpieces are advanced through said retorts.

2. Heat treating apparatus as defined in claim 1 in which said drum comprises an outershell spaced radially outwardly from said retorts, and high temperature insulating material disposed between said shell and said retorts.

3. Heat treating apparatus as defined in claim 1 further including a cylinder centered within and rotatable with said drum and located between said retorts, said distributing area being defined within the interior of said cylinder.

4. Heat treating apparatus as defined in claim 3 in which said delivering and distributing means comprise a conveyor for delivering said workpieces from outside of said chamber and into the interior of said cylinder through one of the ends thereof, a series of angularly spaced holes formed through said cylinder and spaced axially from the discharge end of said conveyor, holes formed through said retorts and alined with the holes in said cylinder, and means within said cylinder and operable as an incident to rotation of the cylinder to advance said workpieces along the cylinder from the discharge end of said conveyor and toward said holes whereby the workpieces drop into consecutive retorts as the latter move beneath said cylinder.

5. Heat treating apparatus as defined in claim 4 in which said conveyor discharges said workpieces into said cylinder at a position located forwardly of said holes, said means within said cylinder advancing said workpieces reversely toward said holes, and said means within said retorts advancing said workpieces forwardly through said retorts.

6. Heat treating apparatus as defined in claim 5 in which said means within said cylinder comprise a series of vanes spaced angularly around and spiraled along the interior of the cylinder, there being one vane associated with each of the holes in the cylinder.

7. Heat treating apparatus as defined in claim 6 in which said means within said retorts comprise augerlike screws, there being one screw located within each retort.

8. Heat treating apparatus as defined in claim 3 in which said drum comprises an outer shell, a ring of high temperature insulating material lining said shell and spaced radially outwardly from said cylinder whereby an annular space is defined between said ring and said cylinder, said retorts being located within said annular space with their outer sides substantially tangent to the inner side of said ring and with their inner sides substantially tangent to the outer side of said cylinder.

9. Heat treating apparatus as defined in claim 8 in which adjacent sides of adjacent retorts are substantially tangent to one another, said retorts being arranged in a circle within said annular space.

10. Heat treating apparatus as defined in claim 1 in which said heating means comprise radiant heating elements located within said chamber adjacent the ends of said retorts, and means for circulating gas past said heating elements and through said retorts.

11. Heat treating apparatus as defined in claim 10 in which radiant heating elements are located at each end of said chamber adjacent the ends of said retorts. I

12. Heat treating apparatus comprising a walled enclosure defining a chamber, a series of generally cylindrical retorts disposed within said chamber and spaced angularly about a generally horizontal axis, said retorts being located with their axes extending substantially parallel to said horizontal axis, mechanism for causing said retorts to revolve in unison about said horizontal axis, means operable to deliver workpieces into retorts from outside of said chamber, means within said retorts for advancing said workpieces through the retorts as the latter revolve about said horizontal axis, and means within said chamber for heating said workpieces as the workpieces are advanced through said retorts.

13. Heat treating apparatus as defined in claim 12 in which said retorts are arranged in a circle around said axis and are located with adjacent sides of adjacent retorts substantially tangent to one another.

14. Heat treating apparatus as defined in claim 13 further including a cylindrical drum surrounding said retorts, the outer sides of said retorts being substantially tangent to the inner side of said drum. 

1. Heat treating apparatus comprising a walled enclosure defining a chamber, a drum supported within said chamber to rotate about a substantially horizontal axis, a cluster of generally cylindrical retorts telescoped rigidly into and spaced angularly around said drum and located with their axes extending substantially parallel to the axis of the drum, said retorts being spaced radially from the axis of said drum thereby to leave a central distributing area between the retorts, mechanism for rotating said drum thereby to cause said retorts to revolve around the axis of the drum, means operable during rotation of said drum to deliver workpieces into said distributing area from outside of said chamber and to distribute said workpieces into said retorts, means within said retorts for advancing said workpieces through the retorts as the latter revolve about the axis of said drum, and means within said chamber for heating said workpieces as the workpieces are advanced through said retorts.
 2. Heat treating apparatus as defined in claim 1 in which said drum comprises an outer shell spaced radially outwardly from said retorts, and high temperature insulating material disposed between said shell and said retorts.
 3. Heat treating apparatus as defined in claim 1 further including a cylinder centered within and rotatable with said drum and located between said retorts, said distributing area being defined within the interior of said cylinder.
 4. Heat treating apparatus as defined in claim 3 in which said delivering and distributing means comprise a conveyor for delivering said workpieces from outside of said chamber and into the interior of said cylinder through one of the ends thereof, a series of angularly spaced holes formed through said cylinder and spaced axially from the discharge end of said conveyor, holes formed through said retorts and alined with the holes in said cylinder, and means within said cylinder and operable as an incident to rotation of the cylinder to advance said workpieces along the cylinder from the discharge end of said conveyor and toward said holes whereby the workpieces drop into consecutive retorts as the latter move beneath said cylinder.
 5. Heat treating apparatus as defined in claim 4 in which said conveyor discharges said workpieces into said cylinder at a position located forwardly of said holes, said means within said cylinder advancing said workpieces reveRsely toward said holes, and said means within said retorts advancing said workpieces forwardly through said retorts.
 6. Heat treating apparatus as defined in claim 5 in which said means within said cylinder comprise a series of vanes spaced angularly around and spiraled along the interior of the cylinder, there being one vane associated with each of the holes in the cylinder.
 7. Heat treating apparatus as defined in claim 6 in which said means within said retorts comprise auger-like screws, there being one screw located within each retort.
 8. Heat treating apparatus as defined in claim 3 in which said drum comprises an outer shell, a ring of high temperature insulating material lining said shell and spaced radially outwardly from said cylinder whereby an annular space is defined between said ring and said cylinder, said retorts being located within said annular space with their outer sides substantially tangent to the inner side of said ring and with their inner sides substantially tangent to the outer side of said cylinder.
 9. Heat treating apparatus as defined in claim 8 in which adjacent sides of adjacent retorts are substantially tangent to one another, said retorts being arranged in a circle within said annular space.
 10. Heat treating apparatus as defined in claim 1 in which said heating means comprise radiant heating elements located within said chamber adjacent the ends of said retorts, and means for circulating gas past said heating elements and through said retorts.
 11. Heat treating apparatus as defined in claim 10 in which radiant heating elements are located at each end of said chamber adjacent the ends of said retorts.
 12. Heat treating apparatus comprising a walled enclosure defining a chamber, a series of generally cylindrical retorts disposed within said chamber and spaced angularly about a generally horizontal axis, said retorts being located with their axes extending substantially parallel to said horizontal axis, mechanism for causing said retorts to revolve in unison about said horizontal axis, means operable to deliver workpieces into retorts from outside of said chamber, means within said retorts for advancing said workpieces through the retorts as the latter revolve about said horizontal axis, and means within said chamber for heating said workpieces as the workpieces are advanced through said retorts.
 13. Heat treating apparatus as defined in claim 12 in which said retorts are arranged in a circle around said axis and are located with adjacent sides of adjacent retorts substantially tangent to one another.
 14. Heat treating apparatus as defined in claim 13 further including a cylindrical drum surrounding said retorts, the outer sides of said retorts being substantially tangent to the inner side of said drum. 